This invention is a joint to be used with pipe or fittings for water and sewer systems and the like. However, it is specifically designed for use with fittings. The major objective of the invention is to provide a reliable seal with an improved assembly method with the incorporation of a restraint system.
Over the last century at least, many different systems for forming a pipe joint or fitting having a joint have been developed, especially for pipes of larger diameter. Generally, these joints are of the bell and spigot type. Two main types are in use today with some variants. These are the push-on joint fitting and the mechanical joint fitting. They are readily understandable by the manner in which they are assembled.
The assembly process of prior known systems is as follows:
Push-On Joint Fittings: (See for example, U.S. Pat. No. 3,963,298 and U.S. Pipe, Field Lok.TM. brochure) The pipe end and the socket are first cleaned, removing any debris or paint build-up. The gasket, which is usually shipped separately, is then placed inside the socket in the gasket seat by looping the gasket and forcing it into place, compressing the gasket slightly in the circumferential direction which causes the gasket to remain in place.
The plain end of the pipe must then be provided with a beveled or tapered end in order to push it past the gasket in the fitting. A pipe, which can be cut in the field, must have its end beveled by grinding prior to insertion into the socket.
It is now necessary to attach a jacking mechanism to the pipe end and the fitting bell in order to force the tapered end of the pipe past the gasket until the pipe bottoms out in the socket. It takes a considerable force to insert the pipe end past the gasket and with short lengths of pipe, control during the insertion becomes quite a problem. The short piece of pipe tends to buckle out of alignment during the force application, hence the necessity for complicated special rigging to provide this force in a controlled way.
In order to reduce the force required, the beveled end of the pipe and the gasket surface in the socket are now lubricated with a soft soap.
The pipe end is then placed carefully into the socket, placing the beveled end on the gasket surface. The pipe end is then jacked into the socket to the depth marked on the pipe surface. The jacks are then removed.
In some cases, joint restraint is provided by special gaskets with steel clips, molded into the gasket. In these cases, the joint must be jacked in the reverse direction after assembly to insure that the clips have locked onto the pipe. If disassembly is necessary, thin shims must be hammered into the joint to lift the clips out of their locked positions prior to jacking the joint apart with the special rigging.
The assembly of these previously known push-on fittings can be a complicated and somewhat time consuming process. For this reason, the major portion of the fittings market is not push-on joint fittings, but rather mechanical joint fittings.
Mechanical. Joint Fittings: As stated above, the majority of the fittings used in the United States are provided with the Standardized Mechanical Joint conforming to the requirements of ANSI/AWWA C111/A21.11, "Rubber-Gasket Joints for Ductile-iron Pressure Pipe and Fittings".
The mechanical joint consists of a tapered gasket seat, a tapered or "wedge shaped" gasket, and a follower ring or "gland". Both the bell of the fitting and the gland are provided with a flange having axial bolt holes. While regular bolts can be used, special "T-Bolts" are generally used to connect the gland to the bell of the fitting. The number of bolts required depends upon the size of the pipe, ranging from four, on the 3-inch size, and eight, on the 12-inch size, to thirty-two on the 48-inch size pipe.
In assembling the joint, the pipe end and socket are first cleaned. The gland is then placed over the plain end of the pipe with its special compression "lip" pointing toward the end of the pipe. The gasket is then lubricated and stretched over the end of the pipe with its tapered surface toward the end of the pipe. No bevel on the pipe is required. The plain end is then inserted into the socket of the fitting until the end bottoms out in the socket. No special rigging is required. The gasket is then brought forward and inserted into the gasket seat, caulking or pounding it into place if necessary. The gland is now brought into position touching the gasket, and the T-bolts are inserted into the holes of the fitting bell and through the holes in the gland. The nuts are screwed onto the bolts and tightening begins. The bolts must be tightened in a "star" pattern, in order to maintain alignment during tightening. First tightening one bolt then the opposite bolt, 180 degrees from the first, then the bolt 90 degrees from the last one, and so on, until all bolts have at least 75 to 90 ft.-lb. placed on them for sizes 3-inch through 24-inch and more for the larger sizes. This is an arduous and time consuming task and requires experience, skill, and strength on the part of the worker.
A phenomenon exists during the tightening of the T-bolts which makes the task of bringing all bolts within a range of 75 to 90 ft.-lb. of torque very frustrating. As one bolt is tightened, bringing the gland closer to the bell, the adjoining bolts loosen. That is, as tightening proceeds, a bolt is brought to 75 ft.-lb., the next bolt is also brought to 75 ft.-lb., and so on, until all of the bolts have been tightened at least once, the first bolt is then checked, only to find that it is extremely loose. The act of tightening all bolts, even in a star pattern, has loosened some of the bolts. The bolts must be tightened and re-tightened until all bolts are within the range of torque specified. This may ordinarily take five or more repetitions before the torque on all bolts is stabilized.
A second frustrating experience is that after tightening, if the joint is left for about thirty minutes, the bolts will loose torque, due to what is commonly referred to as "cold flow" of the gasket. Although if the original torque level was above the 75 ft.-lb. level the joint will not ordinarily leak, the fact of the loss of torque makes determining the cause of a leak very confusing. It is often very difficult to determine if the bolts were or were not tightened properly.
Most fittings are also installed in a trench, making access to the bolts on the bottom of the joint a problem. The most frequent complaint is a leaky joint caused by loose bolts on the bottom of the joint usually due to the difficulty of getting to these bolts.
One benefit of a mechanical joint is that the joint requires no unusual equipment to assemble. Secondly, if a mistake is made, the mistake at least can be remedied since disassembly is reasonably simple. Disassembly of a push-on joint is complicated, requiring special tools, and often results in having to cut the pipe in order to undo the joint. Although it requires skill and some strength to assemble the mechanical joint, mistakes can be corrected and the use of simple tools has kept the mechanical joint the most used joint for fittings.
Other variants of pipe joints and fittings exist. The prior art patents describe two mechanisms having somewhat similar actions. One is referred to as a "Bayonet locking ring". This bayonet ring is a gland ring having integral protruding segments on its outer surface which interact with like integral segments in the bell of a pipe to retain the ring in the bell. This bayonet ring imparts no forward motion and can usually be rotated by hand. This mechanism is referenced in Bram, U.S. Pat. No. 3,765,706, Oct. 16, 1973. The second mechanism is a "Breech Lock" ring also having integral protruding segments on its outer surface which interact with like segments in the bell to retain the gland ring and also impart forward motion when the ring is rotated. These segments have an inclined surface and can either be an interrupted single thread screw or separate and wedge-like. In this invention, the segments are separate and wedge-like. The breech lock ring is usually used also to compress some type of gasket and must be tightened using more force than can be applied by hand. It can be seen in Kennedy, U.S. Pat. No. 4,402,531, Sep. 6, 1983.